fuel pressure woes

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ben240z
Posts: 15
Joined: Mon Apr 10, 2017 1:19 pm
ECU Model: S80 Pro

fuel pressure woes

Post by ben240z »

Good morning, please can I pose a question to the technically minded people on here in the hope of solving a problem that is driving me nuts.

Am I correct in thinking that on a fuel injected set up with a common fuel rail and in this case 6 yellow peco injectors that the 4 bar fuel pressure is maintained at 4 bar pressure by the weber 4 bar pressure regulator fitted to the end of the fuel rail?

The system runs a low pressure pump to feed a swirl pot then dash 6 hose to an 044 bosch high pressure pump with dash 6 fuel line to the fuel rail and dash 6 fuel line returning to the swirl pot. There is a dash 4 line running from the top of the swirl pot to the tank which has a valve in the filler cap to vent the system.

This set up has worked faultlessly from 2005 ish to 2018 when the gremlins first intermittently appeared. The first problem was no 5 injector stopped firing randomly. This led us down the path of either a faulty injector but replacing the injector made no difference. If the injector was earthed it would fire. Moving the injector from no 5 to no 1 made no difference as it was always no 5 that stopped.
After many attempts to cure the perceived electrical problem without success a fuel pressure gauge went into the line before the pressure reg and this was when we found the pressure rising to 9 bar sometimes on startup from cold and other times when running on the track . Other times it would behave perfectly.

I have changed the fuel tank, fuel pumps, fuel lines, injectors, pressure regulator, wiring loom, ecu DTA S80, cam,crank sensors and throttle pot.

When the engine is running there is plenty of fuel returning to the tank and with the pressure gauge showing 6 bar the other day I slackened of the return line at the bottom of the pressure reg until fuel was running out and the gauge continued to read 6 bar.
If the pumps are switched off/engine stopped and then restarted the fuel pressure will most of the time then read 4 bar until it randomly rises again.

Putting the injector problem to one side my main question is, What can cause the pressure in the fuel rail to rise above the pre set pressure of the regulator?

Thanks in advance Ben
stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
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Location: Norn Iron

Re: fuel pressure woes

Post by stevieturbo »

The FPR should maintain a base pressure relative to intake pressure when it is referenced to the intake, as it should be.

So FP itself will rise and fall, but pressure across the injector should remain a constant.

Are you logging fuel pressure, or is this spurious readings off a gauge ? If logs...post some.

the only thing that will see pressure rise, is a restriction to any discharge.. Certainly randomly throwing all manner of parts at something seems a bit mental.

And a -4 "vent" which should be circulating fuel, may be a bit small.

But post some datalogs of the fuel pressure behaviour.
ben240z
Posts: 15
Joined: Mon Apr 10, 2017 1:19 pm
ECU Model: S80 Pro

Re: fuel pressure woes

Post by ben240z »

Hi Steve, sadly not logging any fuel pressure.

The throwing parts at it has not been random but rather following the logic and advice that has been given on the problem, initially believed to be electrical but subsequently fuel pressure related.

The dash 4 vent/return from the swirl pot to the tank has always been there and worked faultlessly for from 2004/5ish to when the issue started in 2018.

Gauge readings are being taken from a digit Stack gauge in the car and an analogue gauge fitted in the fuel line under the bonnet. Both plumbed into the fuel line at the end of the fuel rail with the regulator immediately afterwards, both of which are new and reading the same with the Stack gauge reading about .1 bar more than the analogue gauge.

With the gauges reading 6 bar in the week when it played up again at llandow and the engine still running I slackened the return line from the regulator off to allow fuel to run out and the gauge reading did not reduce so I can't see how it can be any restriction in the ( new again) return line or return from the swirl pot to the vented tank.

Fuel pressure was rock steady running at llandow for 3 laps then rose to 6 bar and stayed there until I shut the pumps off. restarting the pumps saw 4 bar constant again..

It is neither temp or motion related as it can randomly occur at start up in the garage

I appreciate you answer and now you see the impossible challenge I am facing
stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
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Location: Norn Iron

Re: fuel pressure woes

Post by stevieturbo »

Before much else, Id fit a sensor and start logging FP, just to see what it is doing all the time. If you already have a sensor for the stack gauge, assuming it is a 3 wire sensor you could just tag off it.

But if the return is totally free ( just drain it into a container for a test if the high pressure is doable in the garage ), then it seems the FPR could be at fault.

it is not impossible, just some simple tests and logging.
ben240z
Posts: 15
Joined: Mon Apr 10, 2017 1:19 pm
ECU Model: S80 Pro

Re: fuel pressure woes

Post by ben240z »

Hi Steve, I will get the fuel pressure logged and also have an innovate lc1 that I will get installed and start logging that as well.

I did jury rig the return to go back into the tank as a test to make sure it was clear and it flowed perfectly with the pumps running. so much so that the facet pump could not keep the swirl pot filled..

Appreciate the thoughts and advice
ben240z
Posts: 15
Joined: Mon Apr 10, 2017 1:19 pm
ECU Model: S80 Pro

Re: fuel pressure woes

Post by ben240z »

stevieturbo wrote: Sat Jun 04, 2022 10:57 am Before much else, Id fit a sensor and start logging FP, just to see what it is doing all the time. If you already have a sensor for the stack gauge, assuming it is a 3 wire sensor you could just tag off it.



it is not impossible, just some simple tests and logging.
Yes it is a 3 wire sensor. Can I simply splice the sensor wire and run it to the correct pin out on the ecu or will the ecu also require the sensor ground connected to the ecu sensor grounds?
Sorry for the dumb question

ben
stevieturbo
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Joined: Tue Aug 02, 2011 12:08 pm
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Location: Norn Iron

Re: fuel pressure woes

Post by stevieturbo »

Using one wire should work fine. But you could add a sensor ground if you wanted. Probably wont make much odds to any readings.
ben240z
Posts: 15
Joined: Mon Apr 10, 2017 1:19 pm
ECU Model: S80 Pro

Re: fuel pressure woes

Post by ben240z »

Thank Steve, I will sort that out today and then see what is logged when I run the pumps/engine in the week and hopefully the issue will occur
katana
Posts: 455
Joined: Sun Jan 27, 2013 6:08 pm
ECU Model: S60 Pro
Firmware Version: 29

Re: fuel pressure woes

Post by katana »

Some thoughts - feeding a 044 via a -6 supply is not advised as its much to small. Correct size is 12mm ID for decent gravity feed - too small, and pump will cavitate giving erratic fuel pressures. A 044 flows a LOT of fuel and if the majority of it is being returned to the swirl pot with a Facet trying to add to it, maybe the dash 4 vent is proving to be the restriction, so the whole system is becoming pressurised not just the pump to rail line?
stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
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Location: Norn Iron

Re: fuel pressure woes

Post by stevieturbo »

Whilst I'd agree that-6 is too small for a gravity supply...this should in theory if all pumps are correct be a pressure feed to the 044, so perhaps not so bad. Although under heaviest load the Facet is likely to fall short...this pressure supply could be lost and at the most important time.
Really an 044 should never have anything smaller than a -8 feed...but ideally -10 or 12 whether many do that or not. And a lot of the AN fittings or adaptors to the M18 044 inlet, have woefully small ID holes and should be enlarged.

Although a supply issue would not explain the random high pressure seen. The Facet should only be supplying the fuel the engine is actually consuming at any given time.

When the lift pump is inadequate, it is necessary to return to the swirl tank, and most people do indeed do it this way. So other than creating excessive heat within the main loop/tank.....not a big deal really. If the Facet can circulate enough and out the vent/-4, again not a big deal.

Logs are essential to see exactly how bad the high pressure events are, and if not linked to a restriction on the return, most likely the FPR is at fault.
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